Vulcanization accelerator



Patented Aug. 7, 1945- use. sT T s VULCANIZATION ACCELERATOR George E.P. Smith, Jr., and Edward Carr,

Akron, Ohio, assignors to The Firestone Tire & Rubber Company, acorporation of Ohio No Drawing. Application May 26, 1943, Serial No.488,556

21 Claims.

This invention relates to the vulcanization of rubber, and relatesespecially to a new class or chemical compounds which are valuable 3G".

celerators of the vulcanization of rubber or rubberlike substances.

It is a primary object of the present invention to provide a new classof chemical compounds,

and a method of making thesame.

Another object is to provide a new class of improved rubbervulcanization accelerators of the delayed-action, non-scorchingultra-accelerator type. 1

Another object is to provide a method of vulcanizing rubber, wherebyscorching or PIG-VH1! canization during processing of the rubbercompound is substantially prevented, but extremely rapid vulcanizationis obtained at relatively low vulcanizihg temperatures.

Another dbject is to provide improved rubber compositions posessing theability to vulcanize extremely rapidly at relatively low vulcanizingtemperatures, but substantially free from the tendency of rubbercompositions containing conventional ultra-accelerators to set-up orpre-vulcanize under ordinary rubber processing conditions.

A further object is to provide vulcanized rubber of improved quality,possessing the characteristics of high modulus and tensile, lowhysteresis and a high inherent resistance to deterioration by "flexingor aging.

The above and further objects wil be manifest in the description of theinvention which follows.

It has been found that members ofa new class of chemical compounds arevery effectiv in accelerating the vulcanization of natural or syntheticrubber. ventiently prepared by oxidizing a mixture of a dithiocarbamateand an amine. The preferred compounds or the invention may be preparedby treating an alkaline aqueous mixture of a dithiocarbamate andaprimary alkyl amine or a primary cyclo-alkyl amine with one of thefollowing I oxidizing agents: chlorine, bromine, iodine, hypowhereinBrand R: are alkyl radicals, or together constitute a cyclo-alkyleneradical or a cyclo-dialhlene-on radical, and Re is an alkylradical or acyclo-alkyl radical. Thus. the new compounds are believed to bederivatives or sulien- The new compounds may 'be conamide (HSNHz).Examples of alkyl radicals include methyl, ethyl, propyl, butyl, amyl,hexyl',

heptyl, octyl, decyl, lauryl, benzyl, and similar radicals. Examples ofcyclo-alkyl radicals include cyclohexyl and methyl-cyclohexyl radicals.

Examples of cyclo-alkylene radicals include cyclope'nta-methylene,methyl-cyc'lopentamethylene and cyclo-hexamethylene radicals. Examplesof cyclo-di-alkylene-oxy radicals include cyclodiethylene-oily and.methyl-cyclodiethylene-oxy radicals.

The following specific examples are presented for illustrative purposesonly, and are not to be construed as limiting the invention thereto.

Example 1 A sodium diethyldithiocarbamate solution was formed bygradually adding 10.4 grams of carbon disulflde to a solution of 10grams of diethylamine and 5.5 grams of sodium hydroxide in 150 ml. ofwater. A solution of 11 grams of sodium hydrox-. ide in 100ml. of waterand 67.8 grams of cyclohexylamine were then added to the dithiocarbamatesolution, and the resulting mixture was diluted with water to a volumeof about 500 ml. The cyclohexylamine was'pre sent in the ratio of 5moles per mole of the dithiocarbamate, and the solution contained twomoles of sodium hydroxide per mole of the dithiocarbamate. The mixture,so produced, was maintained at 20-25 C. and agitated during the gradualaddition thereto of an aqueous iodine solution containing 34.8 grams ofiodine and 34.8 grams of potassium iodide in a total of 250 ml. ofsolution. A white, finely divided, crystalline precipitate separatedduring the addition of the last portions of the iodine solution. Thisprecipitate was separated by filtration. washed with water and dried.The product melted at 6465 C. and weighed 21.5 grams,

a yield of 64 per cent 01' N-cyclohexyl (diethylthiocarbamyl)sulfenamide, having the following Analysis of the product showed that itcontained 10.94 per cent of nitrogen and 26.90 per centof sulfur, incomparison with percentages of 11.4 and 28.0, respectively, calculatedfrom the above formula. 4

The oxidation reaction may be represented as follows: y

, to form the thiuram disulfide, as lower temperatures favor theformation of the latter compound.

The sulfenamide derivative was tested as a vulcanization accelerator inthe following rubber formula:

Parts by Ingredients weight Acceleratol: I

The rubber composition, so formulated, was heated for 40 and 60 minutesat 240 F., and the following data were obtained:

Ovo aoo o I ing agent.

These data show that the sulfenamide derivative possesses an appreciabledelayed action, allowing its use, with safety, in rubber compositions tobe processed under usual factory conditions, wherein temperatures ashigh as 230 F, are often reached. '1'

Example 2 Additional sulfenamide derivatives were prepared according tothe method of Example 1 by reacting cyclohexylamine with thedithiocarbamates from dimethylamine, dibutylamine and diamylamine,iodine being utilized as the oxidiz- Thus, N-cyclohexyl(dimethylthiocarbamyl) sulfenamide, a light yellow liquid was preparedina yield of'40 per cent. This compound possesses the following formula:

Modul i l ticittyli 18 'Ilgnsile gtrglllagthn l Accelerator a l o ih5/111 8 ea HsC CHz-Ofia 40min. fio min. 40min. 60min. 5

Likewise from di-n-butylamine there was pro- N- 111 1 th t h i l r lybgllfe duced N cyclohexyl (dl n-butylthiocarbamyl) amide 21325 I 2,900 ,93,950 sulfenan jde The above data show that the sulfenamide 40derivative is a rapid accelerator, impartin ex- CH ceptionally highphysical properties to the vulcanized rubber composition at therelatively low Hlfh r vulcanizing'temperature of 240 F. The sulfen- 45amide derivative was also tested to determine whether or not itpossessed delayed-action characteristics by comparing it with aconventional ultra-accelerator, butyl zimate (zincdibutyldithiocarbamate) in the following rubber formula:

The two rubber compositions were heatedlfor CHg-CH,

a light yellow liquid, in a yield of 78 per cent.

The above three sulfenamide derivatives were tested in the first rubberformula set out in Example 1.

were tested at 10, 30 and 90 minutes at 230 E.

and the following data were obtained:

Modulus of elasticity in lbs/in. at elongation Tensile strength inlbs./in. at break Accelerator Cure in minutes N-cyclohexyl(dimethylthiocarbemyl) sulfenamide... No cure I, 325 No cure..- 3, 7003,3568% groke at N-cyclohexyl (dibutylthioearbamyl) sulfenamide do 8252, 775 do 2, 950 0 so and 60 minutes at 230 n, andthe following datewere obtained:

The above data show that the dimethyl and dibutyl derivatives are veryeflective delayed- 5 action ultra-accelerators. The dl-aniyl deriva- Thedimethyl and dibutyl derivatives tive was tested at 40, so and 90minutes at 2%" and the following data were obtained:

A solution of sodium cyclopentamethylenedi-thiocarbamate was preparedfrom piperidine, carbon disulfide and sodiumhydroxide solution. Portionsof this solution were separately condensed with cyclohexylamine,isopropyl'amine, secondary amylamine and tertiary amylamine, by the useof an iodine oxidizing solution, to form sulfenamide derivatives. Thesewere, in order, N- cyclohexyl (cyclopentamethylenethiocarbamyl) a whitecrystalline solid, melting at 74.5-75.5 (2.,

and analyzing 25.14 per cent of sulfur, compared Example 4 In accordancewith the method of Example 1, sodium diethyldithiocarbamate was reactedwith isopropylamine to produce a 43 per cent yield of N-isopropyl-(di-ethylthiocarbamyl) sulfenamide,

C-S.-NCH-CH; H503 H H; v a light yellow liquid. Likewise, the samedithiocarbamatewas reacted with sec. amylamine to form N-sec. amyl(diethylthiocarbamyl) sulfenamide,

' li-C-S-N-CH-CHrCHa-CH:

H6O; H; a light yellow liquid. In a siinilar manner, sodiumdimethyldithiocarbamate was condensed with isopropylamine' at -50 C. toform a per cent yield of N-isopropyl (dimethylthiocarbamyl) sulfenamide,

mc N-C-S-N-CH-OH;

also a light yellow liquid. All of these sulfenamide derivatives aredelayed-action ultra-accelerators comparable to previously discussedmembers of the preferred class.

to 24.8 per cent calculated from the formula; N-isopropyl(cyclopentamethylenethiocarbamyl) sulfenamide,

CHr-C H: I C\z N :-si I-cH-om Gin-on, s H H.

a white crystalline solid, melting at 50-52 0., N-sec. amyl(cyclopentamethylenethiocarbamyl) sulfenamide,

' clan-cm or N-methyl-n-propylca'rbin (cyclopentamethylenethiocarbamyl)sulfenamide, a light yellow ;liquid; and N-tert. amyl(cyclopentamethylenethiocarbamyl) sulfenamide,

CHECK: OH:

' containing thecyclohexyl derivative, in the first rubber formula setout in Example 1, and heated for 20 and 45 minutes at 270 F.:

Modulus of elmticity in lbs./in. at elongation of 600% Tensile strengthin IbsJInJ-at v break.

Accelerator Cure in minutes N-cyclohexyl (cyclopentamethylenethiovcarbamyl) sulienamide 675 2,350 2,750 3,850

Example 5 A solution was prepared containing 42.3 grams (0.23 mole) ofsodium cyclodi-ethylene-oxydithiocarbamate (from morpholine, carbondisulfide and sodium hydroxide), 67 grams (1.13 moles) of isopropylamineand 9.1 grams (0.23 mole) of sodium hydroxide in a volume of 500 ml. An

aqueous iodine solution containing 58 grams (0.23 mole) of iodine and 58grams of potassium iodide in. a volume of 400 ml. was dropped into thedithiocarbamate solution at room temperature (25? C.), with stirring.The product separated as a white crystalline solid, 15.8 grams (32 percent yield), melting at 79-80 C. After one recrystallization frompetroleum ether the product melted at 80-81 C. The compound so producedwas N-isopropyl (cyclodi-ethylene-oxythiocarbamyl) sulfenamide, havingthe following formula:

GH -CH2 O N-C-S-N-CH-CH:

CHr-C a S H H:

In a similar manner, the dithiocarbamatefrom morpholine was reacted withsec. butylamine to produce a 36 per cent yield of the lightamber liquidproduct, N-sec. butyl -(cyclodi-ethyleneoxythiocarbamyl) sulfenamide,

Likewise, the dithiocarbamate from morpholine was reacted with sec.amylamine to produce a 37 per cent yield of the amber liquid product,N-sec. amyl (cyclodi-ethylene-oxythiocarbamyl) sulfen- In addition, thesame 'dithiocarbamate was reacted with cycloh'exylamine to produce a 50per cent yield of N-cyclohexyl (cyclodi-ethylene-oxythiocarbamyl)sulfenamide,

which, after recrystallization from petroleum ether consisted of whitecrystals melting at 85- The above sulfenamide derivatives frommorpholine are all effective delayed-action accelerators of thepreferred class of compounds. The following test data for the cyclohexylderivative, in the first rubber formula set out in Example 1, ispresented as typical of this group of compounds. The rubber compositionwas heated for 40, 60, 90 and 120 minutes at the low vulcanizingtemperature of 240,F.

Sodium di-octyldithiocarbamate was prepared from a commercial sample ofdi-octylamine, carbon ,disulfide and sodium hydroxide. To complete thereaction, the mixture was heated to 60 C. and a slight excess of carbondisulflde was added. As the. dithiocarbamate salt was partiallyinsoluble in water, sufficient alcohol was added to bring it intosolution. Four moles of isopropylamine were added per mole of thedithiocarbamate, and the resulting mixture was oxidized with iodinesolution. The product at first precipitated as a liquid, and thensolidified in the form of white pellets, having a melting. point of55-60 C. The preparation was obtained in a yield of 93 per cent of thetheoretical yield for N-isopropyl (di-octylthiocarbamyl) sulfenamide,

' the new compound so prepared.

ber, reclaimed rubber or synthetic rubber, and consistently produce veryrapid-curing compositions. which in the vulcanized state possessunusually high modulus, tensile and abrasion-resisting properties. Thevarious synthetic rubbers vulcanizable by heating'with sulfur are hereinconsidered equivalent to rubber, examples being butadiene polymers,isoprene polymers and various interpolymers of conjugated diolefins andvinyl compounds, such as Buna S (copolymer of butadiene and styrene) andBuna N (copolymer of butadiene and acrylonitrile). Although sulfur hashereinabove been mentioned as the preferred vulcanizing agent, otherknown vulcanizins agents susceptible to acceleration are contemplate-d.

The preferred class of sulfenamide derivatives may be prepared by othermethods than those mentioned above, although the method herein ofoxidizing a mixture of a dithiocarbamate and ammonia or an amine havinga hyrapid or specific vulcanizing properties.

of dilaurylamine,carbon disulflde and sodium hy-' droxide. Thedithiocarbamate was reacted in water solution with four molecularproportions of isopropylamine and iodine to produce a white, crystallineproduct melting at 150-165 C., in a yield of 15 per cent of thetheoretical yield for N-isopropyl (dilaurylthiocarbamyl) sulfenamlde,

' The above two isopropyl derivatives are eflective delayed-actionaccelerators, comparable in drogen atom .attached to the nitrogen atomis preferred. However, the invention is not limited to chemicalcompounds prepared in accordance with any particular method, butincludes the preferred class of compounds, however they may have beenformed.

In addition to the above-enumerated desirable properties imparted by thenew accelerators to rubber compositions, it has been found that thevulcanized compositions also are highly eflicient, having low hysteresischaracteristics. When compared to conventionally accelerated vulcanizedrubber compositions, the new compositions are found to be unusuallyresistant to deterioration upon flexing or aging.

Conventional accelerator activators may 2e employed to an advantage withthe new class of accelerators when extremely rapid vulcanization isdesired, especially at low temperatures. Also, the new accelerators maybe used in combination with other accelerators, such as a guam'dine (e.5., diphenyl guanidine) or a conventional mercaptothiazole derivative(e. g., mercaptobenzothiazole or dibenzothiazyldisulfide) in order toproduce rubber compositions having especially The new accelerators maybe employed in other proportions than the proportions shown, but willnormally be utilizedin the range of .0.1 to 10 parts per parts .ofrubber.

Modification may be resorted to and obvious chemical equivalentssubstituted in the specific examples of the invention without departingfrom the spirit or scope of the invention as defined in the app claims-What is claimed is:

1. The method 01' vulcanizing rubber which includes heating rubber andsulfur in the presence of N-cyclohexyl (diethylthiocarbamyl)sulfenamide.

2. A vulcanizable rubber composition including sulfur and N-cyclohexyl(diethylthiocarbamyl) sulfenamide.

3. A vulcanized rubber product prepared by heating rubber and sulfur inthe presence of N- cyclohexyl (diethylthiocarbamyl) sulfenamide.

4. The method of vulcanlzing rubber which includes heating rubber andsulfur in the presenoe of N-cyclohexyl (cyclopentamethylene-'thiocarbamyl) sufenamide.

5. A vulcanizable rubber composition including sulfurand N-cyclohexyl(cyclopentamethylenethiocarbamyl) sulfenamide.

6. A vulcanized rubber product prepared by heating rubber and avulcanizing'agent in the presence of a substance having the formula;

heating rubber and sulfur in the presence of N- cyclohexyl(cyclopentamethylenethiocarbamyl)' sulfenamide.

7. The method of vulcanizing rubber which includes heating rubber and avulcanizing agent in the presence ofa substance having the formula,

wherein R1 and It: are selected from the group consisting of alkylradicals, a cyclo-alkylene radical and a cyclodi-alkylene-oxy radical,and

R3 is selected from the group consisting of alkyl radicals andcyclo-alkyl radicals.

8. A vulcanizable rubber composition including avulcanizing agent and asubstance having the wherein R1 and R2 are selected from the groupconsisting --of alkyl radicals, -a cyclo;alkylene radical and a'cyclodi-alkylene-oxy radical, and R3 is selected from the groupconsisting or. alkyl radicals and cyclo-alkyl radicals.

is the residue of a Primary amine stronger than ammonia.

13. The process .of vulcanizing rubber. which comprises heating rubberand sulfur in the presence of a compound possessing the structure whereR is :a secondary amino group and Y is a cyclohexyl group. i

14. The. process-of vulcanizing'rubber whic comprises heating rubber andsulfur in the pres- 9. A vulcanized rubber product prepared-by whereinR1 and R: are selected from the group consisting of alkyl radicals, acyclo-alkylene radical and a cyclodi-alkylene-oxy radical, and R3 isselected from the group consisting of lk mcals and cyclo-allcylradicals.

10. The process or vulcanizing rubber which comprises heating rubber andsulfur in the presence of a thiocarbamyl primary amino sulfide.

lL'The process of vulcanizing rubber which comprises heating rubber andsulfur in the presence of a thioca'rbamyl primary amino sulfidepossessing the structure R-S-Rl' where R is a thiocar-bamyl group and Risfthe residue of a primary aminestronger than ammonia.

. 12. The process of vulcanizing rubber which comprises heating rubberand-sulfur in the presence of a compound possessing the structure whereR is a secondary amino-group and the group n N-Y '30 I I -whereI't is asecondar amino group and the oup i ence of dimethyl'thiocarbamylcyclohexylan'fino sulfide.

15. The vulcanized rubber product obtained by heating rubber and sulfurin the presence of a thiocarbamyl primary amino sulfide.

16. The vulcanized rubber product obtained by heating rubber andsulfurinthe presence of a thiocarbamyl primary amino sulfide possessing thestructure RS--R where R is a thiocarbamyl group audit is the residue ofa primary amine strongerthan ammonia.

17. The'vulcanizd rubber product obtained by heating rubber and sulfurin the presence of compound possessing the structure v v -.-'-'Y v e isthe residue ofa' primary amine stronger than ammonia.

" 18. The vulcanized rubber product obtained by heating'rubber andsulfur in the presence of a compound possessing the structure 'where Ris a secondary amino group and Y is a Sulfide.

GEORGE E. P. SMITH, JR. EDWARD L. CARR.

